Thyrotoxic periodic paralysis
Periodic paralysis - thyrotoxic; Hyperthyroidism - periodic paralysisThyrotoxic periodic paralysis is a condition in which there are episodes of severe muscle weakness. It occurs in people who have high levels of thyroid hormone in their blood (hyperthyroidism, thyrotoxicosis).
Muscle weakness
Weakness is reduced strength in one or more muscles.
Read Article Now Book Mark ArticleHyperthyroidism
Hyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often called overactive thyroid.

Causes
This is a rare condition that occurs only in people with high thyroid hormone levels (thyrotoxicosis). Men of Asian or Hispanic descent are affected more often. Most people who develop high thyroid hormone levels are not at risk of periodic paralysis.
There is a similar disorder, called hypokalemic, or familial, periodic paralysis. It is an inherited condition and not related to high thyroid levels, but has the same symptoms.
Hypokalemic
Hypokalemic periodic paralysis (hypoPP) is a disorder that causes occasional episodes of muscle weakness and sometimes a lower than normal level of p...
Read Article Now Book Mark ArticleRisk factors include a family history of periodic paralysis and hyperthyroidism.
Symptoms
Symptoms involve attacks of muscle weakness or paralysis. The attacks alternate with periods of normal muscle function. Attacks often begin after symptoms of hyperthyroidism have developed. Hyperthyroid symptoms may be subtle.
Paralysis
Muscle function loss is when a muscle does not work or move normally. The medical term for complete loss of muscle function is paralysis.

The frequency of attacks varies from daily to yearly. Episodes of muscle weakness may last for a few hours or several days.
The weakness or paralysis:
- Comes and goes
- Can last from a few hours up to several days (rare)
- Is more common in the legs than the arms
- Is most common in the shoulders and hips
- Is triggered by heavy, high-carbohydrate, high-salt meals
- Is triggered during rest after exercise
Other rare symptoms may include any of the following:
-
Difficulty breathing
Difficulty breathing
Breathing difficulty may involve:Difficult breathing Uncomfortable breathingFeeling like you are not getting enough air
ImageRead Article Now Book Mark Article - Speech difficulty
- Swallowing difficulty
- Vision changes
People are alert during attacks and can answer questions. Normal strength returns between attacks. Muscle weakness may develop over time with repeated attacks.
Symptoms of hyperthyroidism include:
- Excessive sweating
- Fast heart rate
-
Fatigue
Fatigue
Fatigue is a feeling of weariness, tiredness, or lack of energy.
Read Article Now Book Mark Article - Headache
-
Heat intolerance
Heat intolerance
Heat intolerance is a feeling of being overheated when the temperature around you rises. It can often cause heavy sweating. Heat intolerance usually...
Read Article Now Book Mark Article - Increased appetite
- Insomnia
- More frequent bowel movements
- Sensation of feeling a strong heartbeat (palpitations)
Palpitations
Palpitations are feelings or sensations that your heart is pounding or racing. They can be felt in your chest, throat, or neck. You may:Have an unpl...
ImageRead Article Now Book Mark Article - Tremors of the hand
- Warm, moist skin
- Weight loss
Exams and Tests
The health care provider may suspect thyrotoxic periodic paralysis based on:
-
Abnormal thyroid hormone levels
Hormone levels
Blood or urine tests can determine the levels of various hormones in the body. This includes reproductive hormones, thyroid hormones, adrenal hormon...
ImageRead Article Now Book Mark Article - A family history of the disorder
- Low potassium level during attacks
- Symptoms that come and go in episodes
Diagnosis involves ruling out disorders associated with low potassium.
The provider may try to trigger an attack by giving you insulin and sugar (glucose, which reduces potassium level) or thyroid hormone.
The following signs may be seen during the attack:
- Decreased or no reflexes
-
Heart arrhythmias
Arrhythmias
An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm. The heart can beat too fast (tachycardia), too slow (bradycardia), or irregul...
ImageRead Article Now Book Mark Article -
Low potassium in the bloodstream (potassium levels are normal between attacks)
Potassium
This test measures the amount of potassium in the fluid portion (serum) of the blood. Potassium (K+) helps nerves and muscles communicate. It also ...
ImageRead Article Now Book Mark Article
Between attacks, the examination is normal. Or, there may be signs of hyperthyroidism, such as an enlarged thyroid changes in the eyes, tremor, hair and nail changes.
The following tests are used to diagnose hyperthyroidism:
- High thyroid hormone levels (T3 or T4)
T3
Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism (the many processes that control the rate...
ImageRead Article Now Book Mark ArticleT4
T4 (thyroxine) is the main hormone produced by the thyroid gland. A laboratory test can be done to measure the amount of free T4 in your blood. Fre...
ImageRead Article Now Book Mark Article - Low serum TSH (thyroid stimulating hormone) levels
TSH (thyroid stimulating hormone) level
A TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It prompts the thyroid g...
ImageRead Article Now Book Mark Article -
Thyroid uptake and scan
Thyroid uptake and scan
A thyroid scan uses a radioactive iodine tracer to examine the structure and function of the thyroid gland. This test is often done together with a ...
ImageRead Article Now Book Mark Article
Other test results:
- Abnormal electrocardiogram (ECG) during attacks
ECG
An electrocardiogram (ECG) is a test that records the electrical activity of the heart.
ImageRead Article Now Book Mark Article - Abnormal electromyogram (EMG) during attacks
EMG
Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.
ImageRead Article Now Book Mark Article - Low serum potassium during attacks, but normal between attacks
A muscle biopsy may sometimes be taken.
Muscle biopsy
A muscle biopsy is the removal of a small piece of muscle tissue for examination.

Treatment
Potassium should also be given during the attack, most often by mouth. If weakness is severe, you may need to get potassium through a vein (IV). Note: You should only get IV if your kidney function is normal and you are monitored in the hospital.
Weakness that involves the muscles used for breathing or swallowing is an emergency. People must be taken to a hospital. Serious irregularity of heartbeat may also occur during attacks.
Irregularity of heartbeat
An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm. The heart can beat too fast (tachycardia), too slow (bradycardia), or irregul...

Your provider may recommend a diet that is low in carbohydrates and salt to prevent attacks. Medicines called beta-blockers may reduce the number and severity of attacks while your hyperthyroidism is brought under control.
Acetazolamide is effective at preventing attacks in people with familial periodic paralysis. It is usually not effective for thyrotoxic periodic paralysis.
Outlook (Prognosis)
If an attack isn't treated and the breathing muscles are affected, death can occur.
Chronic attacks over time can lead to muscle weakness. This weakness can continue even between attacks if the thyrotoxicosis is not treated.
Thyrotoxic periodic paralysis responds well to treatment. Treating hyperthyroidism will prevent attacks. It may even reverse muscle weakness.
Possible Complications
Untreated thyrotoxic periodic paralysis can lead to:
- Difficulty breathing, speaking, or swallowing during attacks (rare)
- Heart arrhythmias during attacks
- Muscle weakness that gets worse over time
When to Contact a Medical Professional
Call the local emergency number (such as 911) or go to the emergency room if you have periods of muscle weakness. This is especially important if you have a family history of periodic paralysis or thyroid disorders.
Emergency symptoms include:
- Difficulty breathing, speaking, or swallowing
- Falls due to muscle weakness
Prevention
Genetic counseling may be advised. Treating the thyroid disorder prevents attacks of weakness.
References
Hollenberg A, Wiersinga WM. Hyperthyroid disorders. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 12.
Kerchner GA, Ptacek LJ. Channelopathies: episodic and electrical disorders of the nervous system. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2016:chap 99.
Selcen D. Muscle diseases. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 393.
-
Thyroid gland - illustration
The thyroid gland, a part of the endocrine (hormone) system, plays a major role in regulating the body's metabolism.
Thyroid gland
illustration
Review Date: 1/26/2020
Reviewed By: Brent Wisse, MD, board certified in Metabolism/Endocrinology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.